Conversion of sec-butyl alcohol (2-butanol or SBA) to methyl ethyl ketone (MEK) can be accomplished by vapor phase catalytic dehydrogenation of the alcohol at high temperature over metal oxide using a series of adiabatic reactors. Because the reaction is highly endothermic, the process stream is reheated between stages.
The dehydrogenation was conventionally carried out in furnace tubes packed with brass turnings. Later the process was changed to employ a series of adiabatic reactors packed with metal oxide deposited on calcined coke. The process stream was initially heated to 715-825° F. (380-440° C.) in the lead furnace. The stream was reheated in the second and third furnaces prior to being passed through the corresponding reactors. Overall conversions of 80-92 mol % were obtained with selectivities of SBA converted to MEK of 94-98 mol %.
The reaction is commercially valuable and constant attempts to improve conversion, selectivity, run time, and the like, are always being made. One of such attempts included the addition of liquid water to the dehydrogenation section feed stream in order to reduce the production of heavy end byproducts. This improved the selectivity to MEK but with some loss of activity and conversion.
The present inventors have determined that coke formed in the furnace tubes can build and spall with a result that coke particulates can appear in the heavier co-product fractions of the downstream product purification section. The present inventors have also surprisingly discovered that the injection of steam into the furnace coils reduces the problem of coke generation and subsequent spalling of coke particulates. In preferred embodiments, continuous injection of steam selectively added into only the last furnace coil in the SBA to MEK conversion section resulted in one or more of (i) lowered tube metal temperatures; and (ii) reduction of coke formation, with minimal impact on overall unit conversion.
In addition it has also been discovered that the presence of coke in the furnace tubes can initiate a corrosion mechanism called Metal Dusting, particularly when tube metal temperatures are in the range 795-1112° F. (424-600° C.). Accordingly, the present inventors also believe that application of the present invention can mitigate Metal Dusting.